Patent Application
20210336556
The present invention relates to a power converter including a three-level power conversion circuit, and is suitable as a power converter for railway systems.
A three-level power converter can divide a direct current power supply voltage with two sets of smoothing capacitors, and can select and output three types of potentials, including positive, negative, and intermediate potentials, of the direct current power supply voltage. Accordingly, this is a power converter used in a case where a direct current power supply voltage is high, or in a case where a harmonic of a voltage and a current applied to an alternating current load or an alternating current power supply to be connected is desired to be reduced.
PTL 1 discloses a technique of reducing a withstand voltage of a device involved in charging and reducing the size and cost of the device by providing an initial charging circuit for a smoothing capacitor included in a power converter, which includes a three-level PWM converter and a PWM inverter.
With a switching operation of a semiconductor device constituting a main circuit, a noise current flows to a frame of a power unit via a stray capacitance between the semiconductor device and the frame. The frame of the power unit and the power converter are conducted via an attachment portion, making the noise current flow out to the power converter. In addition, since the power converter is connected to a vehicle body via a ground circuit, the noise current that flows to the outside of the power converter also flows out to the vehicle body. When this noise current flows out to the vehicle body, there is a problem that a high-frequency potential variation is caused in the vehicle body and a failure occurs in a signal device.
In order to solve the above problems, a power converter according to the invention includes a three-level power conversion circuit, in which a frame to which a semiconductor device constituting the three-level power conversion circuit is attached is electrically connected to a neutral point of the three-level power conversion circuit.
According to the invention, the frame to which the semiconductor device constituting the three-level power conversion circuit is attached is electrically connected to the neutral point of the three-level power conversion circuit. Thereby, the noise current generated from the three-level power conversion circuit can be drawn back to the three-level power conversion circuit, and the noise current flowing out to the outside of the power converter can be reduced.
Hereinafter, first and second embodiments according to the invention will be described with reference to the drawings as modes for carrying out the invention.
A power converter 1 includes a converter power unit 2, which is a three-level power conversion circuit, and an inverter power unit 3. The power converter 1 is mounted, for example, for an alternating current vehicle, and takes in a single-phase alternating current power from an alternating current overhead line via a pantograph 15 by passing the power through a vacuum alternating current contactor 14 and lowering the voltage with a main transformer 13.
The alternating current power taken into the power converter 1 passes through an electromagnetic contactor 9 or 10 and is then rectified by the converter power unit 2. The rectified direct current power is taken into the inverter power unit 3, and the alternating current power obtained by conversion is supplied to a main motor 4 and controlled.
Further, in the power converter 1, the inverter power unit 3 and the converter power unit 2 are three-level circuits, and have a configuration in which a neutral point is grounded. Regarding the grounding of the neutral point, in
As a semiconductor device constituting the converter power unit 2 and the inverter power unit 3, semiconductor device 5 and clamp diodes 6 that perform a switching operation as a main circuit are attached to frames of the power units. In addition, on the other hand, it is also general that a cooler for the power unit is attached to each frame of the power units as shown in, for example,
In addition, regarding the semiconductor device constituting the converter power unit and the inverter power unit, as the semiconductor devices that perform a switching operation as a main circuit, IGBT, hybrid SiC (a combination of IGBT and a SiC Schottky barrier diode), or full SiC is adopted.
Further, although
A power converter 17 (whose outline is in solid line shown in
Specifically, as shown in
Here, in the invention, by adopting a configuration in which the frame to which the semiconductor devices constituting the three-level power conversion circuit are attached is electrically connected to the neutral point of the three-level power conversion circuit, a noise current generated from the three-level power conversion circuit is drawn back to the three-level power conversion circuit, and the noise current can be prevented from flowing out to the outside of the power converter. The configuration shown in
With the above configuration, the noise current, which flows to the frame 18 of the power unit (and the cooler) along with a potential variation caused by the switching operation of the semiconductor devices 19 to 22 constituting the main circuit, passes through the noise absorbing core 29 back and forth and then flows to the neutral point 27 of the three-level inverter via the ground resistor 11, as indicated by the dotted line of the arrows in
The noise absorbing core 29 is a ferrite core, and by flowing a current into the core, the magnetic energy generated by the noise current is converted into heat by the core for consumption, and the noise current is reduced.
As described above, flowing the noise current flowing to the frame 18 of the power unit (and the cooler) to the neutral point 27 of the three-level inverter by using the noise absorbing core 29 is effective means for reducing the noise current. However, the noise absorbing core 29 is not an essential constituent element, and as long as, at a minimum, a configuration in which the frame 18 of the power unit (and the cooler) is connected to the neutral point 27 of the three-level inverter is adopted, it is possible to prevent the noise current from flowing to the power converter 17 and the vehicle body 16.
When configuring the power unit, semiconductor devices 32 are attached to one side of a frame 34 of the power unit, and power unit coolers 33 are attached to the other side. In the invention, along with the potential variation caused by the switching operation of the semiconductor devices constituting the main circuit, the noise current flows to the frame of the power unit via the stray capacitance between the semiconductor devices and the frame. However, by connecting the frame of the power unit to the neutral point of the three-level inverter, the noise current can be positively prevented from flowing out to the vehicle body.
In this way, the wiring 30 electrically connected to the frame 18 and the wiring 28 electrically connected to the neutral point 27 of the three-level inverter are wound around the noise absorbing core 29 for a plurality of times, so that the attenuation effect for the noise current flowing to the frame 18 by the noise absorbing core 29 can be enhanced, and the noise can be further reduced.
As a difference in configuration from the first embodiment, a core is used for reducing the noise in the first embodiment, while a capacitor is used in the second embodiment instead of the core. That is, as shown in
With the above configuration, the noise current flowing to the frame 18 of the power unit (and the cooler) passes through the noise absorbing capacitor 31 and then flows to the neutral point 27 of the three-level inverter via the ground resistor 11, as shown by the dotted line of arrows in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-198131 | Oct 2018 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/038689 | 10/1/2019 | WO | 00 |
